The invention pertains to the treatment of wastewater to remove and to biochemically modify carbonaceous and nitrogenous pollutants. More specifically, the invention provides method and apparatus adapted to upgrade existing secondary treatment wastewater plants in a manner to effect the maximum utilization of existing tankage and other related already paid for equipment.
Wastewater treatment plants currently in use typically include facilities for the removal of grit and screenables followed by sedimentation tanks for removing settleable and floating solids and secondary treatment tanks for the biological removal of carbonaceous matter from the wastewater. Secondary treatment of wastewater is accomplished by providing an environment conducive to the growth of attached biological slimes or activated flocs which utilize the pollutants in the usually presettled wastewater for their natural growth processes.
The secondary treatment of wastewater is accomplished by providing means for bringing the wastewater into contact with the attached slimes or activated flocs so as to supply nutrients and oxygen to the microorganisms. The surplus biological slimes or flocs are subsequently separated from the wastewater thus effecting the necessary clarification. The prerequisites for the effective bioextraction of pollutants from wastewater are, therefore, the continuous supply of nutrients necessary for the maintenance and growth of the microorganisms and oxygen adequate for their respiration. Secondary treatment processes currently in widespread use are known as the activated sludge and trickling filtration methods.
The secondary treatment method known as the activated sludge process, along with such variations as modified aeration and step aeration, has gained widespread use over the past several decades. This process provides for the aeration of the wastewater in the presence of a controlled amount of activated sludge floc relative to the amount of carbonaceous matter applied per unit of time. The microorganisms in the biological flocs extract the pollutants from the wastewater for their nutrition and are supplied with dissolved oxygen from the injection of diffused air into the aeration tank. Pollutants are removed from the wastewater by accretion onto the floc and by conversion into new organism growth which are subsequently separated from the wastewater by settling.
The standard rate or high rate trickling filtration processes provide for passing presettled wastewater over slimes grown on and attached to stationary surfaces. Clarification is effected by removal of carbonaceous matter through the activities of attached biological slimes that are subsequently separated from the clarified liquor.
A third, and very effective biological process for treating wastewater to oxidize carbonaceous matter, utilizes rotating biological contactors in the form of a plurality of closely spaced, partially submerged bodies, on which grow attached biological slimes. The rotating biological contactors can be in the form of thin discs, drums, cylinders, brushes, etc. The partially submerged bodies, are forcibly rotated to alternately expose the organisms on the contact surfaces to the atmosphere for the absorption of oxygen and the wastewater for nutrients.
Representative wastewater treatment systems utilizing a multistage configuration of partially submerged rotating biological contactors for the sequential treatment of wastewater are shown and described in Torpey U.S. Pat. No. 3,575,849; El Naggar U.S. Pat. No. 3,335,081; Simpson U.S. Pat. No. 3,455,241; and Hartmann et al. U.S. Pat. No. 3,389,798.
By a wide margin the vast majority of secondary treatment plants presently in use today are of the activated sludge and trickling filtration type. Although secondary treatment by rotating biological contactors has been shown to be very effective, various technical and economic factors have prevented their widespread utilization. One of the significant factors inhibiting the widespread use of rotating disc secondary treatment plants, is the existing tremendous capital investment already made in activated sludge and trickling filtration plants.
Prior art wastewater treatment systems are primarily concerned with removing carbonaceous pollutants from the wastewater and secondarily with the oxidation or removal of other materials such as soluble nitrogenous compounds, e.g. ammonia and nitrates. Recently, increased attention has been given to the presence of ammonia-nitrogen in receiving waters, particularly where potable water supplies are involved.
The nitrogenous matter in normal wastewater typically comprises a large fraction of ammonia, a smaller fraction of albuminoid nitrogen, and proteinaceous matter. The proteinaceous matter in wastewater exists in particulate form and is removed through coagulation and sedimentation. The ammonia-nitrogen content of normal domestic wastewater is usually from about 20 to about 35 mg/liter.
Processes for removing ammonia-nitrogen from wastewater follow two general lines of approach: (1) the physio-chemical, and (2) the biological. Physiochemical processes generally have the basic disadvantage of being costly, producing undesirable side effects, generating a concentrated brine for disposal, and in some cases, polluting the air with ammonia vapors. The biological processes on the other hand, promote the natural cyling of nitrogen, i.e., oxidation of the ammonia and denitrification of the resulting nitrates to nitrogen gas.
It is a primary objective of the invention to provide a process and related apparatus for the effective removal of carbonaceous matter and the oxidation of nitrogeneous pollutants in normal domestic wastewater. A further objective of the invention is to provide a method for integrating a process of the foregoing type into existing activated sludge and trickling filtration treatment plants in such a manner as to utilize the available tankage and other existing capital equipment to a maximum extent. Additional objectives of the invention will become apparent as the description proceeds.